Synthesis and evaluation of imidazo[1,5-a]pyrazines as corticotropin releasing hormone receptor ligands

A novel series of imidazo[1,5-a]pyrazines was synthesized and evaluated as corticotropin releasing hormone (CRH) receptor ligands. SAR studies focused primarily on dialkylamino side chain optimization. SAR of the aryl and small alkyl substituents was also explored.     

Substrate kringle-mediated catalysis by the streptokinase-plasmin activator complex: critical contribution of kringle-4 revealed by the mutagenesis approaches

Streptokinase (SK) is a protein co-factor with a potent capability for human plasminogen (HPG) activation. Our previous studies [1] have indicated a major role of long-range protein-protein contacts between the three domains (alpha, beta, and gamma) of SK and the multi-domain HPG substrate (K1-K5CD). To further explore this phenomenon, we prepared truncated derivatives of HPG with progressive removal of kringle domains, like K5CD, K4K5CD, K3-K5CD (K3K4K5CD), K2-K5CD (K2K3K4K5CD) and K1-K5CD (K1K2K3K4K5CD). While urokinase (uPA) cleaved the scissile peptide in the isolated catalytic domain (μPG) with nearly the same rate as with full-length HPG, SK-plasmin showed only 1-2% activity, revealing mutually distinct mechanisms of HPG catalysis between the eukaryotic and prokaryotic activators. Remarkably, with SK.HPN (plasmin), the 'addition' of both kringles 4 and 5 onto the catalytic domain showed catalytic rates comparable to full length HPG, thus identifying the dependency of the "long-range" enzyme-substrate interactions onto these two CD-proximal domains. Further, chimeric variants of K5CD were generated by swapping the kringle domains of HPG with those of uPA and TPA (tissue plasminogen activator), separately. Surprisingly, although native-like catalytic turnover rates were retained when either K1, K2 or K4 of HPG was substituted at the K5 position in K5CD, these were invariably lost once substituted with the evolutionarily more distant TPA- and uPA-derived kringles. The present results unveil a novel mechanism of SK.HPN action in which augmented catalysis occurs through enzyme-substrate interactions centered on regions in substrate HPG (kringles 4 and 5) that are spatially distant from the scissile peptide bond.     

Molecular and biochemical aspects of plant terrestrialization

The transition from water to land was a major evolutionary step for the green lineage. Based on fossil data, this event probably occurred some 480–430 million years ago, during the Ordovician and the early Silurian and initiated the explosive evolution that led to the modern diversity of photosynthetic organisms living on Earth. The chronological steps are still puzzling, but the great advances in genetics have allowed some of them to be positioned on the time axis.Chloroplastic organisms evolving towards terrestrialization have had to solve many problems: limited water supply, scarcity of mineral and especially phosphorus, harmful effect of ultraviolet and cosmic rays, pronounced fluctuations of temperature and attacks from new and diversified microbes. Many adaptations, such as the modification of the life cycle (sporophytes, seeds), organ diversification (root and leaves), the appearance of complex phenolic compounds (lignin, flavonoids), vascularization, the accumulation of new compounds (cutin, suberin), the development of specialized cells and the establishment of symbiotic interactions, have all played major roles during the transition from water to land and have resulted in the rich plant biodiversity of today. Some molecular and biochemical aspects putatively associated with land plant emergence are summarized here.     

Nitric oxide-mediated modulation of synaptic activity by astrocytic P2Y receptors

We investigated the mechanism of synaptic suppression by P2Y receptors in mixed hippocampal cultures wherein networked neurons exhibit synchronized Ca²⁺ oscillations (SCO) due to spontaneous glutamatergic synaptic transmission. Pharmacological studies suggested that SCO suppression was mediated by P2Y2/P2Y4 receptors. Immunostaining studies and characterization of ATP/UTP-stimulated Ca²⁺ responses in solitary neurons and astrocytes revealed that the SCO attenuation was effectuated by astrocytes. We demonstrate that nitric oxide released from activated astrocytes causes synaptic suppression by inhibiting neurotransmitter release. Physiological concentrations of ATP and UTP evoked NO production in astrocytes. SCO suppression was considerably diminished by removal of extracellular NO by membrane-impermeable scavenger c-PTIO or by pretreatment of cells with nitric oxide synthase inhibitor L-NAME. The nitric oxide donor DETA/NO effectively suppressed the SCO. ATP/UTP inhibited KCl-induced exocytosis at presynaptic terminals in an NO-dependent manner. In the absence of exogenously added ATP/UTP, both the NO scavenger and NOS inhibitor enhanced the frequency of SCO, implying that astrocytes release NO during spontaneous synaptic activity and exert a suppressive effect. We report for the first time that under physiological conditions astrocytes use NO as a messenger molecule to modulate the synaptic strength in the networked neurons.     

Hepatic transcriptome analysis of hepatitis C virus infection in chimpanzees defines unique gene expression patterns associated with viral clearance

Hepatitis C virus infection leads to a high rate of chronicity. Mechanisms of viral clearance and persistence are still poorly understood. In this study, hepatic gene expression analysis was performed to identify any molecular signature associated with the outcome of hepatitis C virus (HCV) infection in chimpanzees. Acutely HCV-infected chimpanzees with self-limited infection or progression to chronicity were studied. Interferon stimulated genes were induced irrespective of the outcome of infection. Early induction of a set of genes associated with cell proliferation and immune activation was associated with subsequent viral clearance. Specifically, two of the genes: interleukin binding factor 3 (ILF3) and cytotoxic granule-associated RNA binding protein (TIA1), associated with robust T-cell response, were highly induced early in chimpanzees with self-limited infection. Up-regulation of genes associated with CD8+ T cell response was evident only during the clearance phase of the acute self-limited infection. The induction of these genes may represent an initial response of cellular injury and proliferation that successfully translates to a "danger signal" leading to induction of adaptive immunity to control viral infection. This primary difference in hepatic gene expression between self-limited and chronic infections supports the concept that successful activation of HCV-specific T-cell response is critical in clearance of acute HCV infection.